Force Commmander's developer, Ronin Entertainment, used a proprietary engine built for a previous RTS game of theirs called Armor Command. Here's a few screenshots, showing the eerie similarities with FC:
http://www.pcgr.com/reviews/strategy/moreinfo_426.asp)
They sold - get this - around 1500 TOTAL copies of Armor Command. Maybe more by now, but I pity the software shop that devoted ANY shelf space to it.
It came out about the same time as Battlezone, and was annihilated. The packaging for AC was kind of lame, so anyone comparing BZ with AC would generally buy BZ because the packaging was so snazzy. Not to mention that BZ was a fricking GREAT game. I'm playing it AGAIN right now, and if you can go find a copy somewhere, DO IT. Seriously. Don't get BZ2, just get BZ1 and go nuts with it.